Within the railroad industry, end of train (EOT) units (sometimes also referred to as end of train devices, or ETDs) are typically attached at the rear of the last car on a train and typically communicate with a head of train (HOT) device typically located on a lead locomotive or a train or consist. EOT units were originally designed to perform some of the functions previously performed by train personnel located in the caboose. Today, EOT units can perform a variety of functions. EOT units include a pressure sensor to monitor air pressure in the air brake pipe and periodically transmit this information to the HOT device, which displays the information to the train crew responsible for operating the train. EOT units also often include an end-of-train marker light that, in the United States, must meet FRA (Federal Railroad Administration) regulations, in order to alert others to the presence of the end of train at night and under other low light conditions. Two-way EOT units can accept an emergency brake command from the HOT device to open a valve attached to the air brake pipe, which causes a loss of air pressure in the air brake pipe, thereby causing an emergency brake application (which is the most severe application of the brakes). Some EOT units include motion detectors that are used to inform the HOT as to whether, and in some cases in which direction, a train is moving. Other EOT units include GPS receivers that are used to transmit location information pertaining to the end of the train to HOT equipment as discussed in U.S. Pat. No. 6,081,769.
Because the EOT units are located at the end of a train, supplying power to EOT units is an important consideration. As discussed in U.S. Pat. Nos. 5,267,473 and 6,236,185, it is known to supply power to EOT units using batteries or a combination of batteries and air-powered generators connected to the brake pipe. In order to conserve battery power, EOT units are usually configured to power down when the unit has been in a horizontal orientation for a period of time, such as after being removed from a train by train yard personnel.
EOT units usually communicate with the HOT devices using radio-based communications. Because of the nature of modern freight railroading, it should be understood that an HOT device is required to communicate with many different EOT units and vice-versa as consists are formed and broken down. Moreover, it is often the case that several HOT devices and EOT units will be within radio communication distance of each other at one time, such as when a train/consist on which the EOT unit and HOT device are mounted is in a train yard. Thus, there is a need for HOT devices to determine which EOT unit messages are intended for it and vice-versa.
In order to meet this need, conventional EOT devices are assigned unique serial numbers and configured to include this serial number in all outgoing communications, and EOT units having a two-way capability only respond to incoming communications that include the unique serial number for the HOT after the EOT unit has been armed. Similarly, HOT devices have the ability to be configured to ignore messages from all EOT units other than the particular EOT device specified by an operator. “Arming” or “linking” an EOT unit typically requires a person to push an arm button on the EOT unit. This causes the EOT unit to send an ARM request message. When the HOT receives such a message with the correct EOT serial number, the HOT sends an ARM confirm message including the EOT unit's serial number to the EOT unit. The EOT responds with an ARM acknowledge message to complete the process. An operator typically configures an HOT device for a particular EOT unit by setting a thumbwheel or other input device to the unique serial number of the desired EOT unit, which is typically imprinted on the outside of the housing of the EOT unit. Upon receiving such an identifier from the operator, the conventional HOT device will display information from messages transmitted by that particular EOT unit and ignore communications from all other EOT units.